A commonly encountered problem with protease-containing liquid detergents is the degradation of second enzymes in the composition by the proteolytic enzyme. The stability of the second enzyme upon storage in product and its effect on cleaning are impaired by the proteolytic enzyme.
Boric acid and boronic acids are known to reversibly inhibit proteolytic enzymes. A discussion of the inhibition of one serine protease, subtilisin, by boronic acid is provided in Philipp, M. and Bender, M. L., "Kinetics of Subtilisin and Thiolsubtilisin", Molecular & Cellular Biochemistry, vol. 51, pp. 5-32 (1983).
One class of boronic acid, peptide boronic acid, is discussed as an inhibitor of trypsin-like serine proteases, especially in pharmaceuticals, in European Patent Application 0 293 881, Kettner et al., published Dec. 7, 1988.
However, in liquid detergents built with alphahydroxyacid, boric acid and its derivatives appear to complex with the builder and are adversely affected as proteolytic enzyme inhibitors. The proteolytic enzyme then is free to degrade second enzymes in these built liquid detergent compositions. The extent to which the builder complexes with boric acid is believed to be a function of the type of alphahydroxyacid builder, and the type of boric acid derivative which is employed in the composition. For example, the effect is dramatic for boric acid in a protease-containing liquid detergent composition built with citric acid. A second enzyme such as lipase in such a system is degraded by the proteolytic enzyme, rendering the lipase ineffective.
The effectiveness of these boric acid/derivatives can be increased by the addition of a vicinal polyol of the general structure: ##STR1## where R.sub.1 is selected from the group consisting of C.sub.1 -C.sub.6 alkyl, aryl, substituted C.sub.1 -C.sub.6 alkyl, substituted aryl, nitro, and halogen; R.sub.2, R.sub.3 and R.sub.4 are independently selected from the group consisting of hydrogen, C.sub.1 -C.sub.6 alkyl, aryl, substituted C.sub.1 -C.sub.6 alkyl, substituted aryl, halogen, nitro, ester, amine, amine derivative, substituted amine, hydroxyl, and hydroxyl derivative; R.sub.1 and R.sub.3 may be linked via a non-aromatic ring; R.sub.5, R.sub.6, R.sub.7, and R.sub.8 are independently selected from the group consisting of hydrogen, C.sub.1 -C.sub.6 alkyl, aryl, substituted C.sub.1 -C.sub.6 alkyl, substituted aryl, halogen, nitro, ester, amine, amine derivative, substituted amine, hydroxyl, substituted hydroxyl, aldehyde, acid, sulfonate and phosphonate and at least one R.sub.5 -R.sub.8 is R.sub.1. Catechol, 1,2 propane diol and glycerine are preferably not included. The equilibrium constants for the reaction of the two ingredients are: K.sub.1 between about 0.1 and 400 l/mole and K.sub.2 between 0 and about 1000 l.sup.2 /mole.sup.2.
Without meaning to be bound by theory, it is believed that a predominantly 1:1 boric/polyol complex is formed which is capable of binding with the active site (serine) on the proteolytic enzyme. This is believed to be better than, for example, a 1:2 boric/polyol complex. The boric/polyol mixture is believed not to be compromised by the alphahydroxyacid builder like boric acid and its derivatives alone are. The second enzyme is not degraded by the proteolytic enzyme, which has been reversibly inhibited by the boric/polyol mixture. Upon dilution, such as under typical wash conditions, the proteolytic enzyme is no longer inhibited and can function (e.g. to remove protease-sensitive stains from fabrics in the wash).
The importance for protease inhibition of the low K.sub.2 value (below about 1000 l.sup.2 /mole.sup.2) and the importance of 1:1 complexing of the boric:polyol mixture in liquid detergent compositions comprising alphahydroxyacid builder, anionic and/or nonionic surfactant, proteolytic enzyme, and a second enzyme, are not disclosed or taught by the art.
European Patent Application 0 381 262, Aronson et al., published Aug. 8, 1990, mixtures of proteolytic and lipolytic enzymes in a liquid medium are disclosed. The stability of lipolytic enzyme is said to be improved by the addition of a stabilizer system comprising boron compound and a polyol which are capable of reacting with one another, whereby the polyol has a first binding constant of at least 500 l/mole and a second binding constant with the boron compound of at least 1000 l.sup.2 /mole.sup.2.
German Patent 3 918 761, Weiss et al, published Jun. 28, 1990 discloses liquid enzyme concentrate which is said to be usable as a raw material solution for making liquid detergents and the like. The concentrate contains hydrolase, propylene glycol and boric acid or its soluble salt.
U.S. Pat. No. 4,900,475, Ramachandran et al, issued Feb. 13, 1990, discloses a stabilized enzyme-containing detergent containing surface active detergent material, builder salt and an effective amount of enzyme or enzyme mixture selected from the group containing protease and alpha-amylase enzymes. The composition also contains a stabilization system comprised of glycerine, a boron compound and a carboxylic compound with 2-8 carbon compounds.
U.S. Pat. No. 4,537,707, Severson, Jr., issued Aug. 27, 1985 describes heavy duty liquid detergents containing anionic surfactant, fatty acid, builder, proteolytic enzyme, boric acid, calcium ions and sodium formate. The combination of boric acid and formate provides improved proteolytic enzyme stability in the compositions.
European Patent Application 0 080 223, Boskamp et al, published Jun. 1, 1983 describes aqueous enzymatic detergent compositions containing boric acid or an alkali metal borate with a polyfunctional amino compound or a polyol, together with a reducing alkali metal salt.
Similarly in GB 2 079 305, Boskamp, published Jan. 20, 1982, it is disclosed that enhanced enzyme stability can be obtained in a built liquid detergent composition by inclusion of a mixture boric acid and polyol in a weight ratio of more than 1:1, and a cross linked neutralized polyacrylate polymer.
The procedure used to determine thermodynamic constants for boric/polyol complexes is based on .sup.11 Boron NMR as described by Dawber et al in the Journal of Chemical Society, Volume 1, pages 41-56 (1988). Thermodynamic constants for some of the compounds of interest are listed in the above article.